A typical traction elevator includes a car and a counterweight interconnected by a plurality of ropes. The ropes extend over a traction sheave that is driven by a drive machine. The load to be moved by the drive machine is determined by the difference between the load of the car, including passengers and freight, and the load of the counterweight.
It is conventional to provide a counterweight that is equal to the weight of the car plus fifty percent of the full `live` load, referred to as fifty percent balancing. Live load, as used herein, means the load attributable to the passengers and freight. With fifty percent balancing, the maximum load to be moved by the drive machine is fifty percent of the full live load. This occurs when the car is either fully loaded to its maximum capacity, such that the car is heavier than the counterweight, or is empty, such that the counterweight is heavier than the car.
The drive machine is sized to be able to drive the elevator at its nominal speed for both full car and empty car operations. This results in a machine that has power output sufficient to lift fifty percent of the live load through the hoistway at its nominal speed.
The above art notwithstanding, scientists and engineers under the direction of Applicants' Assignee are working to develop elevator systems that provide both the desired performance and are cost effective.